Inherent defects and variation of stoichiometry strongly modifies the electrical properties of various insulating and semiconducting oxides. For instance, while ideally pure NiO is a Mott insulator, the presence of inherent defects renders NiO a semiconducting behavior. NiO, is a well-known p-type semiconductor with a wide band gap (˜3.8 eV), and has been widely investigated for different technological applications including nonvolatile memory devices, super capacitor electrodes, electrochromic devices, gas sensors and photocathodes for solar cells. In particular, capacitor-like metal-NiO-metal structures have attracted tremendous attention in the past decade due to its potential as an ultra-high density and high speed nonvolatile memory based on reproducible electric field induced changes in the resistance of a material, known as resistive switching. Typically, an initial step known as electroformation is employed to the as prepared devices to facilitate resistive switching. Here, electroformation refers to the application of a sufficiently large electric field (>106 V/cm) to the pristine devices, which creates conducting nanofilaments in the insulating host matrix. Besides capacitor-like structures, electroformation on single crystalline oxide heterostructured nanowires has also been demonstrated to exhibit resistive switching characteristics. However, very little is known about the electrical and opto-electrical properties of NiO films in planar structure.
On the other hand, physics of light and development of new light based technologies have attracted tremendous research interest owing to their fundamental and technological significance. For instance, photodetectors with low dark current, fast response and high sensitivity have wide range of applications such as optoelectronic devices, biomedical imaging, optical communications, quantum information technology and remote sensing. Transition of electrons between different energy levels by light absorption is the fundamental operating mechanism of a photodetector. Among the commercially available photodetectors, photomultiplier tube and avalanche photodiode stand out owing to their high sensitivity and fast response. However, the prominent demerits of these detectors are fragility, cost, and bulkiness. In addition, the requirement of high electric bias, additional supply voltage stabilization circuitry and intricate temperature compensation hampers the integration of these detectors into the current circuit technologies such as complementary metal-oxide semiconductor (CMOS) electronics. As an alternative, extensive efforts are underway to develop photodetectors from 1D nanowires, quantum dots, metal oxide nanorods and heterojunctions made of nanocomposites and oxide thin films. Although heterojunctions made of ZnO nanorods and NiO thin films have been demonstrated to exhibit modest photodetector characteristics because of a very large response time and high dark current, photoresponse properties of NiO thin films in the planar structure are not known to date.
Embodiments of the present invention seek to address one or more of the above-mentioned needs.